The hydroformylation reaction is employed on a commercial scale to prepare straight chain and branched chain mixtures of aldehydes and alcohols from olefinically unsaturated hydrocarbons.
For reasons of economic feasibility, improvements in hydroformylation catalysts and procedures are being investigated to achieve increased hydroformylation reaction rates and conversions, and increased selectivity to specific hydroformylation products.
The selective production of straight chain aldehydes and alcohols is particularly desirable. Higher oxo alcohols have become important intermediates for synthesis of biodegradable surface-active agents. Oxo alcohols are highly biodegradable, but the biodegradability is inversely proportional to the proportion of branched chain isomer present in an oxo alcohol mixture. There is continuing development effort to increase alpha-olefin hydroformylation selectivity to linear paraffinic aldehydes and alcohols.
Cobalt carbonyl is a conventional catalyst employed for hydroformylation reaction, but large quantities of branched chain aldehydes are produced with this catalyst. Rhodium carbonyl complexes containing tertiary phosphine or phosphite ligands [Evans et al, J. Chem. Soc. A, 3133 (1968); Pruett and Smith, J. Org. Chem., 34, 327 (1969)] are useful at low pressures and give higher ratios of straight chain to branched chain products. Similar cobalt carbonyl complexes [Slaugh and Mullineaux, J. Organometal. Chem., 13, 469 (1968)] also give more straight chain product, but produce alcohols as the primary products.
More recently developed hydroformylation catalysts and processes achieve some improved selectivity to linear products but still result in a high yield of branched chain aldehyde and alcohol products. Illustrative of recent advances in hydroformylation technology are U.S. Pat. Nos. 3,488,296; 3,652,676; 3,876,672; 3,981,925; and 3,984,486.
U.S. Pat. No. 3,981,925 is particularly pertinent with respect to improved hydroformylation selectivity. The said patent discloses a process for hydroformylation of olefins to aldehydes in the presence of a ligand stabilized platinum halide complex in combination with a Group IVA metal halide. The hydroformylation selectivity of the U.S. Pat. No. 3,981,925 process favors formation of straight chain aldehyde, e.g., in Example 1 the mole ratio of 1-octylaldehyde to 2-methylheptaldehyde product from heptene-1 hydroformylation is 9:1. Also produced are 2.7 mole percent of heptene-2 and heptene-3 isomerization products. A high pressure of carbon monoxide is required to suppress olefin isomerization.
There remains a need for hydroformylation catalysts and processes which provide for olefin conversion to aldehyde products with improved efficiency and selectivity at lower carbon monoxide pressures, and with a concomitant reduction in the yield of isomerization, hydrogenation, and polymerization products.
Accordingly, it is a main object of this invention to provide a novel hydroformylation catalyst which promotes the conversion of olefins to aldehydes with a high rate of reaction and a high level of conversion.
It is a further object of this invention to provide an improved hydroformylation process for converting alpha-olefins to linear aldehydes with improved efficiency and selectivity.